The present invention relates in general to spring couplings, and in particular to a brake-type spring coupling for adjustment gears in motor vehicle seat adjusters, the coupling including a bearing body for a rotary shaft, a brake drum secured to the bearing body around the shaft and defining a cylindrical inner jacket, a helical torsion spring normally frictionally engaging the inner jacket, the spring having inwardly bent hook-shaped portions, a coupling segment supported for rotation around the shaft in the brake drum, a cam element rigidly secured to the shaft and defining at each lateral side thereof abutment surfaces, and a supporting peripheral surface, a pair of follower segments supported for rotation about the shaft for movement between the abutment surfaces and the coupling segment, whereby the hook-shaped end portions of the spring are anchored in the follower segments so as to tension or release the spring in response to the sense of rotation of the coupling segment.
In a known adjustable motor-vehicle seat, the seat frame is mounted on a base frame by means of swingable supports and is vertically adjustable by adjustment gears acting on the swingable supports. A drive gear is arranged at each lateral side of the seat and is rigidly connected to an adjuster shaft supported for rotation on the lower frame. The adjuster shaft projects unilaterally from the base frame and supports both the adjustment gears and the brake spring coupling of the aforedescribed type for actuating the adjustment gears.
A balancing spring for compensating at least a part of the weight of the seat and of the seat user acts on the swingable supports of the seat. If the seat is unoccupied, the force of this balancing spring acts via the cam member which is rigidly secured to the adjuster shaft, against the transfer member connected to the end of the brake spring of the coupling and causes the spring to frictionally engage the inner wall of the brake drum. On the other hand, when the seat is loaded the transfer member swings in opposite direction due to the fact that the force of the balancing spring is overcome and the other transfer segments comes into abutment with the cam rigidly connected to the adjustment shaft. Play required for releasing the helical spring of the brake-type spring coupling is the more increased, the more the individual component parts of the coupling approach the limit of manufacturing tolerances. The excessive play of the braking spring in the coupling is not eliminated even if in the conventional brake-type spring couplings, an intermediate resilient or elastic member is employed.